Low velocity cartridge having total propellant ignition

ABSTRACT

An ammunition round is provided with a high pressure chamber containing the propellant which is contained therein by a piston or pusher sabot having contact with the projectile. The inertia of the projectile is applied against the force of the propellant gasses when the propellant is ignited to delay the release of the propellant gases from the high pressure chamber to a low pressure chamber rearwardly of the projectile until the propellant is entirely ignited.

United States Patent Austin, Jr. [45] Apr. 10, 1973 54] LOW VELOCITY CARTRIDGE HAVING 3,613,584 10/1971 Hendricks ..102 93 TOTAL PROPELLANT IGNITION Primary ExaminerR0bert F. Stahl [75 lnvemor' 2 Austm Castlaon AttorneyI-larry M. Saragovitz, Edward J. Kelly, Herbert Berl and Albert E. Arnold, Jr. [73] Assignee: The United States of America as represented by the Secretary of the Army ABSTRACT [22] Filed. Feb 2 1971 An ammunition round is provided with a high pressure chamber containing the propellant which is contained [2l] Appl. No.: 111,895 therein by a piston or pusher sabot having contact with the projectile. The inertia of the projectile is ap- [52] us CL 102/38 102/92 4 102/93 plied against the force of the propellant gasses when [51] Int Cl 13/16 the propellant is ignited to delay the release of the [58] Fieid 93 92 l propellant gases from the high pressure chamber to a 5 7 low pressure chamber rearwardly of the projectile until the propellant is entirely ignited. [56] Reerences Cited 1 Claim, 2 Drawing Figures UNlTED STATES PATENTS 2l9,l07 9/1879 Merriam ..102/4O pmmgwmoma 3,725,218

INVENTOR WILPCEDH Austin JD- ATTORNEYS LOW VELOCITY CARTRIDGE HAVING TOTAL PROPELLANT IGNITION BACKGROUND OF THE INVENTION the propellant is burned in a case behind the projectile 1 and the hot gases generated thereby expand to propel the projectile from the case and along the gun bore. Where the projectile velocity is only a few hundred feet per second, it is generally impossible to obtain consistent muzzle velocities with conventional cartridges where the length of the case to its diameter is low, as of the order of one to two. This is because the rate of increase of the case volume is so rapid, as the projectile is propelled forwardly therein by the initial ignition, that a variable proportion of the propellant is driven along the gun bore after the projectile without being ignited. Thus, round to round combustion is inconsistent, resulting in a low military efficiency.

To overcome this problem, cartridges incorporating a high-low pressure system have been provided in which the propellant is loaded in a relatively small high pressure chamber screwed into the base of the case. When the propellant is ignited, it remains contained in the high pressure chamber until the pressure generated therein reaches a level which assures that all of the propellant is ignited, then, a brass cap covering the propellant and closing the chamber ruptures at the vents therein, thereby permitting the discharge gases to expand into a low pressure chamber in back of the projectile which is propelled thereby from the case.

SUMMARY OF THE INVENTION It is a principal object of this invention to provide a high-low type of low velocity round wherein release of the propellant gas from the high pressure chamber, where the propellant is ignited, to the low pressure chamber rearwardly of the projectile for forward action thereagainst is delayed by the inertia of the projectile for a period of time which assures complete ignition of the propellant.

It is another object of this invention to provide such a high-low type of low velocity round wherein the period of time during which release of the propellant gas is delayed and the degree of initial impact thereof against the projectile are readily varied according to requirements.

It is a further object of this invention to provide such a high-low type of low velocity round which is economical to manufacture, is simple in construction and is positive in operation.

These objects are obtained in the round according to this invention by locating in the high pressure chamber a piston or pusher sabot which retains the propellant gas therein until it is propelled therefrom.

The piston has contact with but is separated from the projectile so that the inertia thereof, multiplied by the ratio of the cross-sectional area of the large diameter of the projectile to the cross-sectional area of the piston, resists the forward travel thereof from the high pressure chamber. Thereby, the resistance of the augmented inertia to the forward travel of the piston, and the length thereof, delay the release of the gases from the high pressure chamber into the low pressure chamber in back of the projectile until all the propellant is ignited. The period of delay between the time the propellant is ignited and the time that the discharge gases are released into the low pressure chamber, and the degree of the initial impact by the discharge gases against the projectile through the piston, are obtainable as desired 0 by selectively varying the diameter and length of the piston.

Further objects and advantages of the invention will be apparent from the following specifications and the accompanying drawings which are for the purpose of illustration only.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross-section of an ammunition round, according to this invention, shown before discharge; and

FIG. 2 is a view similar to FIG. 1 but showing the relationship of the parts during ignition when the piston is propelled from the cooperating bore and the discharge gases are released thereby from the high pressure chamber into the low pressure chamber.

DESCRIPTION OF A PREFERRED EMBODIMENT Shown in the drawings is a round 12 comprising a case 14 and a grenade 16 inserted into the front end thereof to form a low pressure chamber 18 between the grenade and base 20 of the case. A central bore 22 extends from inside surface 24 of base 20 to an end wall 26 and a primer 28 is installed within a cooperating recess 30 formed in the base from the outside face thereof. Aperture 32 provides communication between recess 30 and bore 22. A cylindrical piston 34 of uniform diameter is received by bore 22 with a sliding fit therewith, which piston comprises a plate 36 fixed to one end and a planar surface 38 formed on the other. Both plate 36 and surface 38 are disposed perpendicular to the central axis of piston 34. Surface 38 is spaced from plate 36 a distance whereby, when piston 34 is located in bore 22 and the plate is in contact with inside surface 24, surface 38 is spaced from end wall 26 thereby forming a high pressure chamber 40 therebetween. The inner end of grenade 16 is in contact with plate 36 when installed in case 14 so that the piston 34 serves as a separate pusher type sabot.

A propellant 42 is loaded into high pressure chamber 40 whereby, when primer 28 is detonated by the firing mechanism of the supporting launcher (not shown), the propellant is ignited and the propellant gases formed thereby act against surface 38 to move piston 34 forwardly with grenade 16 which is propelled thereby from case 14. When surface 38 is located outside of bore 22, during the forward travel of piston 34, the propellant gases expand into low pressure chamber 18 for continued application, at a reduced pressure, against grenade 16. The diameter of piston 34, the length thereof, and consequently the diameter and length of bore 22, are determined by the combustion characteristics of propellant 42. These dimensions are important factors in obtaining constant round to round velocities as they control the period of time during which the propellant is contained in high pressure chamber 40 so that complete ignition is effected and optimum velocity obtained. Through piston 34, the inertia of grenade 16 is applied against the pressure of the propellant gases generated in high pressure chamber 40, thereby retarding the displacement of piston 34 in bore 22 and increasing the time of ignition before the propellant gas is released into low pressure chamber 18. The ratio of the cross-sectional area of grenade 16, at the large diameter thereof, to the area of surface 38 determines the degree to which the inertia of the grenade opposes the force of the propellant gases applied against such surface to thereby retard the propulsion of piston 34 from bore 22. The length of piston 34, obviously, further controls the time period wherein propellant 42 after being ignited is contained within high pressure chamber 40. The area of surface 38 also determines the amount of initial force applied by the propellant gas against grenade l6, and this is important as the fuse system in some grenades are more efficiently armed by heavy initial impact of the propellant force thereagainst while others are better armed by a lower impact force. The length of piston 34 and the diameter thereof can be varied to obtain the desired time delay, for complete ignition of propellant 42, and the desired initial force applied against grenade 16. Once the piston and grenade leave the weapon from which they are fired, the two become separated and the ballistics of the grenade in flight are not interfered with.

In the illustrated embodiment, grenade 16 is of 40mm type, the diameter of piston 34 is 0.804 inches and its length is 0.5 inches. Propellant 42 comprises 3 grains of M9 ignition propellant powder. The maximum pressure achieved in high pressure chamber 40 by ignition of propellant 42 is 8,000 psi and this pressure is reduced to a maximum pressure of 3,500 psi when piston 34 is propelled from bore 22 and the discharge gas is released into low pressure chamber 18. The resulting muzzle velocity of grenade 16 is 275 fps and the standard deviation in velocity, computed from the discharge of a number of rounds 12, is less than 5 fps.

wish it to be understood that 1 do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim:

1. An ammunition round comprising a case having a stepped bore of two different diameters and a base, said base including means for receiving a primer centrally thereof, the bore of lesser diameter being disposed adjacent to said base and in communication with said primer receiving means, the bore of larger diameter being disposed coaxial with said lesser diameter bore and remote from said base, the relative diameters of said bores being dimensioned such that said lesser diameter bore defines a chamber of significantly smaller volume than the chamber defined by said larger diameter bore whereby said lesser diameter bore defines a higher pressure chamber relative to the chamber defined by said larger diameter bore, propellant means disposed in said lesser diameter bore adjacent to said base, a projectile axially disposed in said larger diameter bore to extend thereinto toward said lesser diameter bore, and sabot means disposed within said lesser diameter bore and in contact with said projectile for propelling said projectile axially from said case, said sabot means being dimensioned axially to prevent expansion of gasses produced by sald propellant into said larger diameter bore in response to predetermined axial movement of said projectile from said case. 

1. An ammunition round comprising a case having a stepped bore of two different diameters and a base, said base including means for receiving a primer centrally thereof, the bore of lesser diameter being disposed adjacent to said base and in communication with said primer receiving means, the bore of larger diameter being disposed coaxial with said lesser diameter bore and remote from said base, the relative diameters of said bores being dimensioned such that said lesser diameter bore defines a chamber of significantly smaller volume than the chamber defined by said larger diameter bore whereby said lesser diameter bore defines a higher pressure chamber relative to the chamber defined by said larger diameter bore, propellant means disposed in said lesser diameter bore adjacent to said base, a projectile axially disposed in said larger diameter bore to extend thereinto toward said lesser diameter bore, and sabot means disposed within said lesser diameter bore and in contact with said projectile for propelling said projectile axially from said case, said sabot means being dimensioned axially to prevent expansion of gasses produced by said propellant into said larger diameter bore in response to predetermined axial movement of said projectile from said case. 